The present invention relates to a single lens reflex camera exchangeable lens, and more particularly to an exchangeable lens for use in the camera with T.T.L. light measurement type in which a shutter speed and a diaphragm aperture may be automatically selectively controlled and in which values of exposure factors to be automatically controlled may be indicated prior to the commencement of a stopping down operation.
With a so-called diaphragm-priority-automatic-shutter-speed-control camera in which the shutter speed is automatically controlled, the shutter speed to be controlled may be indicated with a fully open diaphragm aperture, i.e., prior to a stopping-down operation, only if information as to the difference in step between a minimum f-number for the lens and the preset f-number , an output of the light measurement and the information as to the film sensitivity are fed to a computing unit in the camera.
In contrast, with a shutter speed-priority-automatic-diaphragm-control camera in which a diaphragm may be automatically controlled, the f-number to be automatically controlled cannot be indicated prior to a stopping-down operation unless information as to the minimum f-number of the exchangeable lens mounted on the camera body is given. With the shutter-speed-priority-automatic-diaphragm control camera, it has been the general practice to separately provide a special member to transmit information as to the minimum f-number for the exchangeable lens to the camera body and to position this special member between the exchangeable lens and the camera body to thereby provide an indication of the f-number to be controlled prior to a stopping-down operation.
Positioning of this member which transmits information as to the minimum f-number on a lens barrel requires an additional provision of the transmitting member being adapted to transmit the difference in step between the minimum f-number for the lens and a preset f-number, or requires another transmitting member to transmit a preset f-number. Thus, many transmitting members have to be provided on a lens barrel for an exchangeable lens in order to provide these functions.
Generally, the majority of the peripheral portion of a joint surface of an exchangeable lens, for example a bayonet joint, which is to be mounted on a camera body is occupied by optical parts such as lenses and parts associated therewith, such that spatial difficulties arise in positioning many transmitting members in the aforesaid peripheral portion. The provision of additional transmitting members poses a critical problem for the manufacturer of the camera who has supplied specific type bayonets in the market for long periods of time as an old type exchangeable lens can no longer be mounted on a new type camera body, while a new type exchangeable lens cannot be mounted on an old type camera body.
In addition, from an optical viewpoint, the use of many transmitting members should be avoided as their use tends to impose sacrifices and limitations on the optical performance of the exchangeable lens due to addition of new factors in the bayonet portion.